1. Field of the Invention
The present invention relates to an amplifier circuit and a radio receiver, and, more particularly, is suitably applied to a method of reducing noise caused by an operational amplifier while suppressing an increase in current consumption of the operational amplifier.
2. Description of the Related Art
In a radio receiver and the like, IV conversion is performed by using a trans-impedance amplifier to amplify a micro current signal. To reduce noise caused by the trans-impedance amplifier, there is a method of increasing an electric current flowing to the trans-impedance amplifier.
For example, Japanese Patent Application Laid-Open No. H6-342561 discloses an equalizer filter including a variable conductance amplifier, a load resistor, a variable negative resistor, a capacitor, means for detecting the amplitude of output of the filter, and means for controlling, with an electric current, the resistance of the variable negative resistor and a method of controlling the resistance of the variable negative resistor such that the output amplitude detected by the amplitude detecting means coincides with amplitude information set in advance in a resistor.
However, if the electric current flowing to the trans-impedance amplifier is increased to reduce the noise caused by the trans-impedance amplifier, power consumption of the trans-impedance amplifier increases. Further, an area occupied by the trans-impedance amplifier has to be increased.
With the method disclosed in Japanese Patent Application Laid-Open No. H6-342561, the negative resistor can cancel a resistance component of the load resistor connected to an output side of the variable conductance amplifier but cannot reduce the noise caused by the variable conductance amplifier.